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16_Trade-offs.Rmd
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16_Trade-offs.Rmd
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# Trade-offs
**Learning objectives:**
- Understand the Trade-offs between S3, R6 and S4
- Brief intro to S7 (the object system formerly known as R7)
## Introduction
* We have three OOP systems introduced so far (S3, S4, R6)
* At the current time (pre - S7?) Hadley recommends use S3 by default: It's simple and widely used throughout base R and CRAN.
* If you have experience in other languages, *Resist* the temptation to use R6 even though it will feel more familiar!
## S4 versus S3
**Which functional object system to use, S4 or S3? **
- **S3** is a simple and flexible system.
- Good for small teams who need flexibility and immediate payoffs.
- Commonly used throughout base R and CRAN
- Flexibility can cause problems, more complex systems might require formal conventions
- **S4** is a more formal, strict system.
- Good for large projects and large teams
- Used by Bioconductor project
- Requires significant up front investment in design, but payoff is a robust system that enforces conventions.
- S4 Documentation is challenging to use.
## R6 versus S3
**R6** is built on **encapsulated objects**, rather than generic functions.
**Big differences: general trade-offs**
```{r 16-Trade-offs-4, echo=FALSE,fig.align='center'}
knitr::include_graphics("images/16-trade-offs.png")
```
## Namespacing {-}
**Where methods are found?**
- in S3, **Generic functions** are **global** and live in the **global namespace**
- Advantage: Uniform API: `summary`, `print`, `predict` etc.
- Disadvantage: Must be careful about creating new methods! Homonyms must be avoided, don't define `plot(bank_heist)`
- in R6, **Encapsulated methods** are **local**: objects with a **scope**
- Advantage: No problems with homonyms: meaning of `bank_heist$plot()` is clear and unambiguous.
- Disadvantage: Lack of a uniform API, except by convention.
## Threading state {-}
In S3 the challenge is to return a value and modify the object.
```{r}
new_stack <- function(items = list()) {
structure(list(items = items), class = "stack")
}
push <- function(x, y) {
x$items <- c(x$items, list(y))
x
}
```
No problem with that, but what about when we want to pop a value? We need to return two things.
```{r}
pop <- function(x) {
n <- length(x$items)
item <- x$items[[n]]
x$items <- x$items[-n]
list(item = item, x = x)
}
```
The usage is a bit awkward:
```{r}
s <- new_stack()
s <- push(s, 10)
s <- push(s, 20)
out <- pop(s)
# Update state:
s <- out$x
print(out$item)
```
In python and other languages we have structured binding to make this less awkward. R has the {zeallot} package. For more, see this vignette:
```{r 16-Trade-offs-5, eval=FALSE}
vignette('unpacking-assignment')
```
However, this is all easier in R6 due to the reference semantics!
```{r}
Stack <- R6::R6Class("Stack", list(
items = list(),
push = function(x) {
self$items <- c(self$items, x)
invisible(self)
},
pop = function() {
item <- self$items[[self$length()]]
self$items <- self$items[-self$length()]
item
},
length = function() {
length(self$items)
}
))
s <- Stack$new()
s$push(10)
s$push(20)
s$pop()
```
## Method chaining {-}
Useful to compose functions from left-to-right.
Use of the operators:
- S3: `%>%`
- R6: `$`
```{r}
s$push(44)$push(32)$pop()
```
## Umm... what about S7 ? {-}
```{r standards, echo = FALSE, fig.cap = "https://xkcd.com/927/"}
knitr::include_graphics("https://imgs.xkcd.com/comics/standards_2x.png")
```
### Primary references: {-}
* Docs: https://rconsortium.github.io/OOP-WG/
* Talk by Hadley Wickham https://www.youtube.com/watch?v=P3FxCvSueag
## S7 briefly {-}
* S7 is a 'better' version of S3 with some of the 'strictness' of S4.
```
"A little bit more complex then S3, with almost all of the features,
all of the payoff of S4" - rstudio conf 2022, Hadley Wickham
```
* Compatible with S3: S7 objects are S3 objects! Can even extend an S3 object with S7
* Somewhat compatible with S4, see [compatability vignette](https://rconsortium.github.io/OOP-WG/articles/compatibility.html) for details.
* Helpful error messages!
* Note that it was previously called R7, but it was changed to "S7" to better reflect that it is functional not encapsulated!
## Abbreviated introduction based on the vignette {-}
To install:
```{r, eval=FALSE}
# install.packages("remotes")
remotes::install_github("rconsortium/OOP-WG")
```
```{r, eval=FALSE}
library(S7)
dog <- new_class("dog", properties = list(
name = class_character,
age = class_numeric
))
dog
#> <S7_class>
#> @ name : dog
#> @ parent: <S7_object>
#> @ properties:
#> $ name: <character>
#> $ age : <integer> or <double>
```
Note the 'class_character', these are S7 classes corresponding to the base classes.
Now to use it:
```{r, eval = FALSE}
lola <- dog(name = "Lola", age = 11)
lola
#> <dog>
#> @ name: chr "Lola"
#> @ age : num 11
```
Properties can be set / read with '@', with automatic validation ('safety rails') based on the type!
```{r, eval = FALSE}
lola@age <- 12
lola@age
#> 12
lola@age <- "twelve"
#> Error: <dog>@age must be <integer> or <double>, not <character>
```
Note thehelpful error message!
Like S3 (and S4) S7 has generics, implemented with `new_generic` and `method` for particular methods:
```{r, eval = FALSE}
speak <- new_generic("speak", "x")
method(speak, dog) <- function(x) {
"Woof"
}
speak(lola)
#> [1] "Woof"
```
If we have another class, we can implement the generic for that too:
```{r, eval = FALSE}
cat <- new_class("cat", properties = list(
name = class_character,
age = class_double
))
method(speak, cat) <- function(x) {
"Meow"
}
fluffy <- cat(name = "Fluffy", age = 5)
speak(fluffy)
#> [1] "Meow"
```
Helpful messages:
```{r, eval = FALSE}
speak
#> <S7_generic> speak(x, ...) with 2 methods:
#> 1: method(speak, cat)
#> 2: method(speak, dog)
```
"most usage of S7 with S3 will just work"
```{r, eval = FALSE}
method(print, cat) <- function(...) {
print("I am a cat.")
}
print(fluffy)
#> "I am a cat"
```
*For validators, inheritance, dynamic properties and more, see the [vignette!](https://rconsortium.github.io/OOP-WG/articles/S7.html)*
https://rconsortium.github.io/OOP-WG/articles/S7.html
## So... switch to S7 ? {-}
$$
\huge
\textbf{Soon}^{tm}
$$
* Not yet... still in development!
* But consider trying it out:
* To stay ahead of the curve... S7 will be integrated into base R someday!
* To contribute feedback to the S7 team!
* To get "almost all" of the benefits of S4 without the complexity !
* In particular, if you have a new project that might require the complexity of S4, consider S7 instead!
## Meeting Videos
### Cohort 1
`r knitr::include_url("https://www.youtube.com/embed/W1uc8HbyZvI")`
### Cohort 2
`r knitr::include_url("https://www.youtube.com/embed/bzo37PHCM1I")`
### Cohort 3
`r knitr::include_url("https://www.youtube.com/embed/_byYFTQHp1Y")`
### Cohort 4
`r knitr::include_url("https://www.youtube.com/embed/vdKDPBcOc6Y")`
### Cohort 5
`r knitr::include_url("https://www.youtube.com/embed/3EvqtVYTFVM")`
### Cohort 6
`r knitr::include_url("https://www.youtube.com/embed/vEButxFIvLw")`
<details>
<summary> Meeting chat log </summary>
```
00:11:36 Oluwafemi Oyedele: I have not built anything with them!!!
00:16:31 Arthur Shaw: https://cran.r-project.org/web/packages/sp/index.html
00:19:05 Arthur Shaw: Apparently Hadley asked the same question we're asking several years ago: https://stackoverflow.com/questions/5437238/which-packages-make-good-use-of-s4-objects
00:19:16 Trevin: HA
00:23:54 Trevin: Your audio is breaking up Federica
01:06:58 Federica Gazzelloni: https://mastering-shiny.org/reactive-motivation.html?q=R6#event-driven
01:07:37 Federica Gazzelloni: https://engineering-shiny.org/common-app-caveats.html?q=R6#using-r6-as-data-storage
01:10:52 Oluwafemi Oyedele: Thank you !!!
```
</details>
### Cohort 7
`r knitr::include_url("https://www.youtube.com/embed/2vxnzqWp-OU")`